German Published Patent Application No. 199 56 789 describes a planetary gear, which is designed to be attached to an electric motor and has a compact construction. In particular, a sealing element, which seals the sun-wheel shaft from the external space, is situated on an outer diameter that is reduced in comparison with the receiving region for the output shaft of the electric motor, which means that the heat generation may be reduced. In this context, it may be disadvantageous that the bearing for the sun-wheel shaft is far away from the motor to be attached. In addition, it may be difficult and expensive to satisfactorily true the output shaft for the planetary gear. And, despite the reduction in diameter, the heat generation in the sealing element and bearing 28 is considerable at high input speeds, such as those which often occur in servo drive units. It may also be disadvantageous that the sealing element is difficult to lubricate, since it is separated from the interior of the gear by bearing 28. The planet carrier does form a bearing seat for bearing 30, but it is interrupted, because the bores for the planet bolts must be provided. This may have a negative effect on the rigidity and torsional stiffness. The planet carrier is supported against the gear housing and therefore requires a large, expensive bearing 30. Since bearings 30 and 32 are positioned in the shape of an X, the imaginary bearing spacing of bearings 30 and 32 is small, and, therefore, only correspondingly small, transverse forces are allowed. In the case of low gear ratios i, i.e., a large sun gear, it may be difficult and, under some circumstances, even impossible to mount the sun gear.
It is an aspect of the present invention to provide a planetary gear, which may be used for connection to an electric motor, which may have a compact construction, and which may be more efficient and/or powerful. In addition, the planetary gear may be more cost-effective in view of overall economics, as well as simple to manufacture, without requiring high expenditure.